Calculating Minimum Power for Perception of Radiation from a Point Source

[jasmin_89]

Homework Statement

Power source of radiation

Relevant Equations

Is my solution correct?

Hallo, can anybody help me and check if i have the right result:

What is the minimum power P that a point source of radiation (I=8*10^(-7) W/m^2) at a distance of l=10 m from the listener must have in order to still be perceived? (Note: The emitted energy per area can be related to a spherical body with A=4 π r^2)

P=I*A
P=8*10^-7 (W/m^2)*4*pi *(10m)^2= 0,001 Watt

 

[Filip Larsen]

Your result looks correct to me.

Small nitpick: If no other constraints are given I would probably write the result as 1.0⋅10^-3 W or just 1.0 mW to better signal the number of significant digits in the result.

 

[jasmin_89]

Ok, thank you :)